Circuits for decoding additional information in a composite signal serve to recover additional information from received signals in audio or video consumer equipment. As a rule, the additional information represents auxiliary information which makes it easier for the user to operate the respective receiver. For a car driver, for example, the identification of a receiver station as a traffic information station represents important information. Similar additional information is contained in television signals, which include digital information as to whether the respective sound channel is a mono signal, a stereo signal, or a multichannel sound signal.
Via additional carriers or by multiplexing existing carriers, this information is inserted as an AM or FM signal into the existing composite signal. Decoding this additional information is generally simple and can be readily implemented with conventional analog circuits or, after analog-to-digital conversion, with conventional digital circuits. However, the rapid changes of such additional information and the continual introduction of new additional information present difficulties, because under certain circumstances the switchovers controlled by the additional information are greatly disturbed by adjacent channels and poor receiving conditions and result in misinterpretations of the additional information.
It is therefore an object of the invention to provide a circuit for decoding such additional information included in a composite signal which is less susceptible to noise and spurious effects.